2 to n optical divider with integrated optics

ABSTRACT

A 2 to n divider with integrated optics, where n is an integer greater than or equal to 2, including at least one 2 to 2 optical divider element in a substrate. The optical divider element comprises a first and a second guide with widths equal to W 1  and W 2 , respectively. The first and second guides are suitable for dividing an input light wave input into one of the guides, into a first and second output wave transported by the first and second guides respectively according to a determined division ratio. These first and second guides have at least three parts. A first part where the first and second guides move toward each other, a second part where the first and second guides are approximately parallel to each other and a third part where the first and second guides gradually separate from each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority to U.S. provisionalapplication No. 60/427,923 filed Nov. 21, 2002, and to application no.0213747 filed Nov. 4, 2002 in France, the entire contents of each ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a 2 to n optical divider withintegrated optics. More particularly, it relates to an optical dividerthat may find use in the field of optical telecommunications, such as,in the 1260-1360 nm and 1480-1660 nm spectral windows.

2. Description of Related Art

A 2 to n optical divider (where n is an integer greater than or equal to2) includes at least one optical divider element comprising 2 inputs and2 outputs to divide a light wave injected into one of the inputs into 2parts. The light is distributed to each of the outputs with a predefineddivision ratio.

When n is more than 2, the optical divider comprises several cascadeddivider elements so as to have 2 inputs and n outputs and enable thedistribution of a light wave injected into one of the two inputs, to then outputs according to a predefined division ratio for each of theoutputs.

U.S. Pat. No. 5,835,651 describes a conventional 2 to 2 divider.

FIG. 1 diagrammatically shows a conventional 2 to 2 divider of this typemade with integrated optics, in the xy plane of the substrate containingthe divider.

In this figure, the substrate in which the divider is made is not shown.FIG. 1 shows first and second single-mode input wave guides 1 and 3,first and second single-mode output wave guides 5 and 7 and a dual-modewave guide 9 with length La along the x axis and width Wa along the yaxis. The dual-mode wave guide 9 connects the input wave guides and theoutput wave guides. The input and output wave guides are connected tothe dual-mode guide at an angle β from the x axis.

With this divider, a light wave Ea injected into one of the single-modeinput guides, for example guide 1, propagates in the guide in thedirection of the dual-mode guide 9 and becomes closer to the secondinput guide 3, thus, setting up a proximity coupling with the secondinput guide. This proximity coupling is greater for higher wavelengths(such as wavelengths within the 1480-1660 nm spectral band) than forlower wavelengths (such as wavelengths in the 1260-1360 nm spectralband).

At the end of the single-mode input guides 1, 3, the light wave iscoupled to the two modes of the dual-mode guide 9. The spectral behaviorof coupling between these two modes during propagation in the dual-modeguide is contrary to the behavior in single-mode guides. In other words,coupling for higher wavelengths (1480-1660 nm) is weaker than for lowerwavelengths (1260-1360 nm).

At the output from the dual-mode guide 9, the light wave is coupled witha given distribution onto the two single-mode output guides 5, 7. Thelight wave is once again affected by proximity coupling, until thesingle-mode guides have separated by a distance H such that the lightwave propagating in each single-mode guide no longer sees theother-guide.

As a result, a light wave Ea is distributed into two light waves S1 a,S2 a in the two single-mode output guides 5, 7.

The spectral behavior in the single-mode input and output guides that iscontrary to the spectral behavior in the dual-mode guide, allows thecreation of a 2 to 2 achromatic divider in the dual-mode guide, forselected values of β, Wa and La. For example, a low value of β limitsexcess losses.

Although it is satisfactory in some respects, that the light wave inthis 2 to 2 divider be affected by a discontinuity at each end of thedual-mode guide connected to the single-mode guides creating mismatchlosses between the modes of the dual-mode guide and the modes of thesingle-mode guides, and reflection losses. These mismatch and reflectionlosses are particularly annoying for applications in the opticaltelecommunications field.

Moreover, as shown previously, excess losses and achromatism depend onβ. On one hand, β must increase to reduce chromatism. On the other hand,β must decrease to reduce excess losses. This behavior of the dividermakes it difficult to make a 2 to 2 divider with good achromatism andlow excess losses.

BRIEF SUMMARY OF THE INVENTION

An aspect of embodiments of this invention is to provide a 2 to noptical divider with integrated optics without the limitations anddifficulties of conventional dividers.

In particular, one aspect of embodiments of the invention is to providea 2 to n divider with low excess losses and satisfactory achromatism,particularly for optical telecommunications in all of the 1260-1360 nmand 1480-1660 nm spectral windows. The divider, according to oneembodiment of the invention, is advantageously very slightly chromaticor even achromatic, and has minimum excess losses.

In the remainder of the description, achromatic refers to either lowchromatism (for example <0.5 dB for telecommunications spectral windows)or “perfect” achromatism.

A further aspect of the invention is to make a 2 to n divider in whichexcess losses and chromatism are independent to facilitate itsapplication.

Another aspect of the invention is to provide a 2 to n divider withoutany discontinuities for the light wave so as to limit mismatch andreflection losses.

In one embodiment of the invention, the 2 to n divider with integratedoptics, with n being an integer greater than or equal to 2, comprises atleast one 2 to 2 optical divider, element in a substrate. This elementcomprises a first and a second guide, with widths equal to W1 and W2respectively, suitable for dividing an input light wave E input in oneof the guides, into a first and second output wave S1 and S2 transportedby the first and second guides, respectively. These first and secondguides have at least three parts:

a first part, of a first coupling type, in which the first and secondguides progressively move towards each other, until a distance Dc thatis not zero and is less than a threshold distance Ds corresponding tothe minimum distance starting from which the input light wave input intoone of the guides can be at least partly coupled in the other guide,

a second part, of a second coupling type, with length Lc, called thecoupling length, in which the guides are approximately parallel to eachother and are distant by the value Dc, and

a third part, of a first coupling type, in which the guides graduallyseparate starting from the value Dc until they are separated by a valueof more, than Ds.

The values Dc, Lc, W1 and W2 are chosen so as to obtain an achromaticdivider element at the divider operating wavelengths. The values Dc andLc are chosen so that the first coupling type and the second couplingtype vary inversely with the wavelengths.

The light wave is divided with a division ratio CR related to the outputof one of the first or second guides (by convention).

In the present description, an optical guide is a guide with lateralconfinement, unlike a planar guide in which light can propagate within aplane (the guide plane).

The optical guides according to one embodiment of the invention arepreferably single-mode.

An optical guide is composed of a central part generally called the coreand media surrounding the core that may be identical to each other ordifferent from each other.

To enable confinement of light in the core, the refraction index of themedium from which the core is made must be different and in most casesgreater than the refraction index of the surrounding media.

To simplify that description, the guide will be considered to consist ofthe central part of the core. Furthermore, all or part of thesurrounding media will be called the substrate. However, one of ordinaryskill in the art would understand that when the guide is not buried oris only slightly buried, one of the surrounding media may be outside thesubstrate and may for example be air.

The substrate may be a single-layer or a multi-layer, depending on thetype of technique used.

Furthermore, depending on the application, an optical guide in asubstrate may be more or less buried in the substrate and particularlymay comprise portions of the guide buried at variable depths. This isparticularly true in the technology for ion exchanges in glass.

According to one embodiment, the divider is made with integrated opticsin a glass substrate using ion exchange techniques.

According to one embodiment of the invention, dedicated particularly totelecommunications applications, the first and the second guides havewidths W1 and W2 such that the behavior of the divider element based onDc and Lc is achromatic in the operations spectral windows from 1260 to1360 nm and from 1480 to 1660 nm.

We will usually choose W1=W2=W.

Preferably, the guides become closer to each other and/or separate fromeach other symmetrically.

Excess losses C may be defined using the following equation:

C=10 log (P _(S1) +P _(S2))/P _(E)

where P_(S1), P_(S2), P_(E) are the powers of waves S1, S2 and E,respectively.

The choice of values Dc, Lc, W1 and W2 provides a means for compensatingfor light coupling phenomena between the two guides that are differentdepending on the wavelengths, and thus create an achromatic dividerelement.

When the distance D between the guides is more than the value Ds, thereis no coupling between the guides. When the distance D between theguides is between the distance Ds and a distance Dx, the guides set up aweak proximity coupling that is greater for high wavelengths (forexample 1480-1660 nm) than for low wavelengths (for example 1260-1360nm). On the other hand, when the distance D between the guides becomessmaller and is between Dx and Dc, the operating conditions are changedand the phenomenon involved is then a strong proximity coupling that isweaker for higher wavelengths (for example 1480-1660 nm) than for lowerwavelengths (for example 1260-1360 nm). This strong proximity couplingis made particularly on the length Lc of the second part.

Furthermore, since Dc is not zero, the light wave is not affected by anydiscontinuity in this divider element, which results in very smallexcess losses. In one preferred embodiment, Dc must be greater thanDmin, where Dmin=0.5 μm.

The value Dx can be defined as being the distance separating the twoguides starting from which the proximity coupling is inverted fromstrong to weak and vice versa.

The 2 to 2 divider element made according to the invention may beconsidered as comprising two types of proximity couplers; a first typeof coupler operating globally in the weak coupling conditions,corresponding to parts I and III of the divider itself if strongcoupling zones can exist in these parts, depending on the value of Dx;and a second type of coupler operating in the strong coupling conditioncorresponding to part II of the divider.

Moreover, in parts I and III of the divider element corresponding toweak coupling, the guides can be brought close to each other and/orseparated from each other moving along an arc of a circle with a radiusR>Rc. The value Rc is defined as being the critical radius of curvatureabove which there are no longer any curvature losses at the highestwavelength in the spectral window considered (for example 1260-1360 nmand 1480-1660 nm). This value Rc is defined in order to minimize excesslosses of the 2 to 2 divider element.

In one of the embodiments, the radius R will be taken equal to Rc inorder to minimize weak proximity coupling.

Furthermore, as R becomes smaller, the divider element will become morecompact. Therefore there is a two-fold advantage in choosing R=Rc.

In the case of a 2 to n divider with integrated optics, where n is aninteger greater than 2, this divider comprises a 2 to 2 optical dividerelement in the substrate like the one described above, and n−2 cascaded1 to 2 divider elements such that the divider comprises 2 inputscorresponding to the 2 to 2 divider element input guides and n outputs.

The 1 to 2 divider elements are selected from among Y couplers orjunctions These divider elements may or may not be symmetric.

An asymmetric divider element may be obtained in case of a coupler, byvarying the coupler interaction length and/or the selection of thedifferent coupler output channels.

An asymmetric divider element may be obtained in the case in which a Yjunction is used by varying the section of the output channels from thejunction and/or the angle between the output channels from the junctionand the optical axis of the junction input channel.

Other specific features and aspects of the invention will becomeapparent when taken with the detailed description and examining theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, already described, diagrammatically shows a known 2 to 2divider;

FIG. 2 diagrammatically shows a section through a 2 to 2 divideraccording to an embodiment of the invention;

FIG. 3 diagrammatically shows graphs useful for setting parameters forthe Dc, W and Lc characteristics of the divider element according to anembodiment of the invention;

FIG. 4 diagrammatically shows the spectral response of the device inFIG. 2;

FIG. 5 diagrammatically shows a first variant embodiment of a 2 to ndivider, where n is greater than 2; and

FIG. 6 diagrammatically shows a second variant embodiment of a 2 to ndivider when n is greater than 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 diagrammatically shows an example of a 2 to 2 divider formed by a2 to 2 divider element according to the invention, capable of dividing alight wave E into two parts S1 and S2 with a division ratio of CR.

This diagram shows a partial section of a substrate 10 in an xy planecontaining the different propagation directions of the light waves E, S1and S2 in the optical guides of this element.

This divider element comprises first and second, for example,single-mode guides, G1 and G2 in the substrate 10. In this example, thewidths W of these guides are identical. They are combined together so asto divide an input light wave E input into one of the guides (forexample G1) into first and second output waves S1 and S2 with a divisionratio CR. The wave S1 is transported by guide G1 and the wave S2 istransported by guide G2. If the light wave E is input into the dividerfrom the guide G2, then the guides G1 and G2 provide waves S1 and S2 ontheir outputs with a division ratio CR. These waves may be differentfrom the waves produced by the divider when the wave E is input by theguide G1.

Guides G1 and G2 each have at least three parts:

a first part I in which the guides G1 and G2 gradually move towards eachother until the distance Dc that is not zero and is less than athreshold distance Dx corresponding to the minimum distance from whichthe input light wave E input into one of the guides sees the otherguide,

a second part II with length Lc called the coupling length in which theguides G1 and G2 are parallel to each other and are not equal to thevalue Dc, and

a third part III in which the guides gradually move away from the valueDc to a value of more than Ds.

The values Dc, Lc and W are selected so as to have an achromatic dividerelement at operating wavelengths.

The distances Ds, Dc, are measured along the y direction of the plane ofthe section in the figure, while the length Lc is measured along the xdirection of this plane.

For a 2 to 2 divider element, excess losses and satisfactory chromatismmean excess losses less than 0.2 dB (particularly for all 1260-1360 nmand 1480-1660 nm spectral windows) and achromatism less than 0.5 dB (forall of these windows).

The invention is applicable to all domains for which a 2 to n opticalfunction is necessary and more particularly to telecommunicationsfields.

In the telecommunications field, operating wavelengths are usuallywithin the 1260-1360 nm and 1480-1660 nm spectral windows.

These optical guides may be made in the substrate using any type oftechnique and particularly ion exchange techniques or deposition andetching techniques. Guides may be delimited by appropriate masking.These techniques are well known in the integrated optics field.

The substrate may be a single-layer substrate or a multi-layersubstrate, depending on the type of technique used. For example, thesubstrate may be glass in the case of ion exchange techniques.

With this type of divider, a light wave E input into the guide G1propagates in the guide G1 moving gradually towards the guide G2, thuscreating a coupling of proximity with the guide G2 as soon as thedistance between guides G1 and G2 is less than the threshold value Ds(where Ds is the minimum distance at which the two guides see each otherat the operating wavelengths considered). As long as the distance Dbetween the two guides G1 and G2 is not too small, the phenomenoninvolved is a weak proximity coupling which is greater for highwavelengths (for example 1480-1660 nm) than for low wavelengths (forexample 1260-1360 nm). On the other hand, when the distance D betweenthe single-mode guides becomes smaller, the operating conditions changeand the phenomenon involved becomes a strong proximity coupling which isweaker for high wavelengths (for example 1480-1660 nm) than for lowwavelengths (for example 1260-1360 nm).

The change in the operating conditions takes place with the distance Dxbetween, the guides is between the values Ds and Dc.

Thus, in the part I, the proximity coupling between the guides changesfrom zero coupling (when Ds>D>Dx) that is stronger for higherwavelengths than for lower wavelengths. The proximity coupling betweenthe guides then changes from weak coupling (when Ds>D>Dx) to strongcoupling (when Dx≧D≧Dc) which is stronger for low wavelengths than forhigh wavelengths. This strong proximity coupling is maintained in partII in which the distance D between guides G1 and G2 is equal to Dc(Dx≧Dc). Finally, in part III, the coupling changes once again fromstrong coupling (when Dx≧D≧Dc) to weak coupling (when Ds>D>Dx) andsimilarly to above, with a reversal of the coupling behavior for highand low wavelengths. Finally, there is no longer any coupling betweenthe two guides for a distance D between the guides greater than Ds.

Thus, the result is a light wave E distributed in two waves S1 and S2 inthe two single-mode guides G1 and G2. This contrary behavior between aweak proximity coupling and a strong proximity coupling can be appliedto make an achromatic divider element for selected values of Dc, W andLc, as a result of a compensation phenomenon. Moreover, since Dc is notzero in this device, the light wave is not affected by anydiscontinuity, such tat excess losses are very low and dependencebetween excess losses and chromatism is eliminated. Dc is more than 0and in one of the embodiments, Dc must be greater than Dmin where Dminis equal to 0.5 μm.

The free parameters used to modify chromatism are Dc, W and Lc, with Lcbeing less useful as will become clearer from the rest of thedescription. Dc, W and Lc have very little influence on excess losses,thus also making these values and the chromatism independent of eachother. This independence also facilitates implementation of the 2 to 2divider element.

As we have already seen, the guides can be brought closer to each otheralong an arc of a circle with radius R≧Rc, or with a sine type functionwith a radius or curvature R such that R≧Rc. Rc is defined as being thecritical radius of curvature beyond which there are no losses ofcurvature at the highest wavelength of the spectral operations windowsconsidered (for example 1260-1360 nm and 1480-1660 nm), in order tominimize excess losses in the 2 to 2 divider element.

In one of the embodiments, the radius R will be taken equal to Rc inorder to minimize weak proximity coupling. For example, Rc=30000 μm.

The divider element is capable of dividing a wave E into two parts usinga division ratio CR such that:

CR=P _(S2)/(P _(S1) +P _(S2))

with respect to guide G2 (equation 1) or

CR=P _(S1)/(P _(S1) +P _(S2))

with respect to guide G1,

where P_(S1), P_(S2) are the luminous powers of the light waves S1 andS2 respectively.

Furthermore, as already shown, the 2 to 2 divider element made accordingto one embodiment of the invention can be assumed to act like two typesof proximity couplers: a first type of coupler operating globally in theweak coupling conditions corresponding to parts I and III of the dividereven if, depending on the value of Dx, there may be strong couplingzones in these parts; and a second type of coupler operating understrong coupling conditions corresponding to part II of the divider.

In general, for the wave amplitude, the transfer matrix Ti of a couplerI is written as follows: $T_{1} = \begin{Bmatrix}{{\cos \left( {K_{i}L_{i}} \right)}{\sin \left( {K_{i}L_{i}} \right)}} \\{{\sin \left( {K_{i}L_{i}} \right)}{\cos \left( {K_{i}L_{i}} \right)}}\end{Bmatrix}$

Since the divider element of the 2 to 2 invention acts like two couplersplaced one behind the other, if a light wave E is injected into theguide G1, the luminous output power of the guide G2 can be written asfollows:

P _(S2)=(P _(S1) +P _(S2))·[sin(K ₁ ·L ₁)·cos(K ₂ ·L ₂)+cos (K ₁ ·L₁)·sin(K ₂ ·L ₂)]², namely:

P _(S2)=(P _(S1) +P _(S2))·sin²(K ₁ ·L ₁ +K ₂ ·L ₂)  (equation 2)

where K1 and L1 are the parameters fo the effective coupler associatedwith the converging arms in parts I and III, and K2 and L2 are theparameters of the coupler with strong coupling associated with part II.Thus, K1=K_(weak), L1=L_(eff) and K2=K_(strong), L2=Lc. The couplingcoefficients Ki are functions of λ, the width W of the guides and thedistance D separating them respectively.

Therefore, equations 1 and 2 can be used to write the division ratio CR(for example with respect to the guide G2) in the form of a sinusoidalfunction, particularly of Lc:

CR=sin²(K _(weak)(λ, W, D _(eff))·L _(eff) +K _(strong)(λ,W,Dc)·Lc)  (equation 3)

where

K_(weak)(λ, W, D_(eff)) is the proximity coupling coefficient of theweak coupler with effective center to center distance D_(eff) and theeffective length L_(eff) of the divider element that can be associatedwith guides G1 and G2 in the converging parts I and III,

λ is the wavelength of the light wave considered,

K_(strong)(λ, W,Dc) is the proximity coupling coefficient of the strongcoupler with center to distance Dc and length Lc, of the divider elementthat can be associated with part II,

W is the width of the single-mode guides of the 2 to 2 divider element.

The first coupler corresponding essentially to the curved convergencearms in part I and in part III of the guides G1 and G2 has a fairlylarge effective center-to-center distance D_(eff) since it is equal tothe average distance between the converging arms. Consequently, thiscoupler operates in the weak coupling conditions characterized bystronger coupling at high wavelengths than at low wavelengths.Therefore, K_(weak) is an increasing function of λ that depends onD_(eff) and L_(eff). These parameters are directly related to theaverage radius of curvature R of the curved converging arms of guides G1and G2 in parts I and III. Coupling between the converging armsincreases when R increases. Therefore, this coupling can be limited if Ris as small as possible. To limit this coupling (to make R as small aspossible) and also to limit excess losses (R≧Rc), it is advantageous touse R=Rc where Rc is defined as being the minimum radius of curvaturebeyond which there are no curvature losses at the highest wavelength ofthe spectral windows considered.

For example, Rc=30000 μm.

The second proximity coupler corresponds at least to part II in whichthe two guides G1 and G2 are approximately parallel and are at adistance of Dc. In this coupler, the distance Dc must be small so as tohave strong coupling between guides G1 and G2. Thus, this coupleroperates in a strong coupling condition for which coupling is greater atlow wavelengths than at high wavelengths. Therefore, K_(strong) is adecreasing function of λ, unlike K_(weak). The coefficient K_(strong)depends on the parameters W and Dc (when these parameters increase, thecoupling coefficient K_(strong) reduces), and on λ. It is recommendedthat Dc≧Dmin so as to limit any mode mismatch losses.

The contrary variation of K_(weak) and K_(strong) allows to have adivision ratio between the two output arms of the guides G1 and G2 (inpart III) that is only slightly dependent on λ. To achieve this, thevariations of K_(weak) and K_(strong) as a function of λ must beapproximately identical but in opposite directions. Therefore, theparameters that can be varied to obtain this compensation between strongcoupling and weak coupling are Dc and W.

FIG. 3 shows variations for CR as a function of Lc for differentwavelengths for values of Dc=1.2 μm and W=2.8 μm.

These curves were obtained experimentally by varying Lc from 0 to 450 μmfor wavelengths 1260 nm (curve 41), 1360 nm (curve 42), 1480 nm (curve43) and 1660 nm. (curve 44).

Thus, according to equation 1 and as shown in FIG. 3, the division ratioCR between the guide output arms is a sinusoidal function of L_(strong)and therefore of Lc. Therefore, the parameter Lc provides a way toadjust this division ratio. If strong coupling and weak couplingcompensate for a given spectral window, then the variations of CR as afunction of Lc, associated with the wavelengths of this spectral window,are sine curves that are very close to each other, as shown in FIG. 3.As the sine curves become more nearly coincident, the 2 to 2 dividerelement becomes more achromatic. The stucy of CR as a function of Lcprovides a means of defining parameters for the divider element.

If periods of the sinusoidal function CR(Lc) are longer at highwavelengths than at low wavelengths, then the strong coupling zone(essentially part II) overcompensates for the weak coupling zones (partsI and III). In this case, Dc and/or W have to be increased to give goodchromatic compensation between these two zones.

The curves in FIG. 4 illustrate total losses (including excess losses)of the light wave between the input through one of the guides and theoutput of this wave through one of the guides, as a function of thewavelengths, for a 2 to 2 divider element like that shown in FIG. 2.

Thus, losses are sown for a wave E:

input through guide G1 and output through guide G1 (curve E_(G1), S1reference 31),

input through guide G1 and output through guide G2 (curve E_(G1), S2reference 32),

input through guide G2 and output through guide G1 (curve E_(G2), S1reference 33),

input through guide G2 and output through guide G2 (curve E_(G2), S2reference 34).

These curves were obtained for a 2×2 divider element in which Lc=220 μm,CR−0.5. Excess losses of this element are weak and are less than 0.15dB.

It can be seen in FIG. 4 that total losses in the 1260-1360 nm and1480-1660 nm spectral windows do not vary by more than 0.5 dB.Therefore, it can be said that this divider element is very slightlychromatic and has very low excess losses.

According to one advantageous mode, the following can be chosen for a2×2 divider element according to one embodiment of the invention with adivision ratio of 0.5 and operating in the 1260-1360 nm and 1480-1660 nmspectral windows:

guide widths W such that W<Wc, where Wc is the maximum width for whichthe guides are single-mode for wavelengths greater than 1260 nm,

a radius of curvature R of guides in parts I and III such that R=Rc,where Rc is the minimum radius of curvature for which curvature lossesat 1660 nm are not negligible,

Dc and W such that curves showing the variation of the division ratio CRas a function of Lc are coincident for wavelengths within the 1260-1360nm and 1480-1660 nm spectral windows,

Lc such that the division ratio CR is equal to 0.5.

For example, we can choose:

Dc between 0.6 and 2.6 μm,

W between 1.6 μm and Wc,

Lc between 0 and 450 μm.

FIGS. 5 and 6 diagrammatically show a 2 to n divider according to theinvention in the special case of n equal to 4.

These figures illustrate a partial section of the substrate 10, in thexy plane containing the different propagation directions of light wavesin the divider according to the invention.

This divider comprises a 2 to 2 type divider element 15 in the substrate10 like that described with reference to FIG. 2 cascaded with two 1 to 2type divider elements that may or may not be symmetric.

Thus, each of the output ends of the guides G1 and G2 of the element 15is optically connected to a 1 to 2 type divider such that the dividerfinally contains two inputs reference A1 and A1 into which a wave E canbe input, and 4 outputs reference B1, B2, B3, B4 that can output wavesS1, S2, S3, S4 respectively at the output.

FIG. 5 shows two 1 to 2 divider elements made by Y junctions referenced21 and 23, junction 21 being connected to guide G1 while junction 23 isconnected to guide G2. Junction 21 also comprises two output guides G1to output the output wave S1 and G3 to output the output wave S3; thejunction 23 also comprises two output guides G2 to produce the outputwave S2, and G4 to produce the output wave S4.

Division ratios between the different arms of each Y junction differentfrom 0.5 can be obtained by varying the section of junction outputguides and/or the angle between the junction output guides and theoptical axis of the junction input guide.

In FIG. 6, the two 1 to 2 divider elements are made by couplers 25 and27. The coupler 25 is made by guide G1 and a guide G5, part of which islocated close to the guide G1 in order to couple parts of the wavetransported in guide G1, in guide G5. Therefore, guides G1 and G5produce output saves S1 and S3. The coupler 27 is made by the guide G2and a guide G6, part of which is located close to guide G2 to couplepart of the wave transported within guide G2, in guide G6. Therefore,guides G2 and G2 output saves S2 and S4.

Division ratios other than 0.5 between the different coupler outputs canbe obtained by varying the interaction length of the coupler and/or thesection of the different coupler output guides.

What is claimed is:
 1. A 2 to n divider with integrated optics, where nis an integer greater than or equal to 2, including at least one 2 to 2optical divider element in a substrate, said divider element comprising:a first and a second guide with widths equal to W1 and W2 respectively,said divider element adapted to divide an input light wave input intoone of the first and second guides, into a first and second output wave,said first and second output wave transported by the first and secondguides respectively; wherein said first and second guides each compriseat least three parts: a first part, of a first coupling type, whereinthe first and second guides are progressively separated by smallerdistance proceeding from input ends thereof, to a distance Dc that isnot zero and is less than a threshold distance Ds, said distance Dscorresponding to the minimum distance starting from which the inputlight wave input into one of the first and second guides can be at leastpartly coupled into the other guide, a second part, of a second couplingtype, with a coupling length Lc, along which said first and secondguides are substantially parallel to each other and are distant fromeach other by the value Dc, and a third part, of the first couplingtype, in which the first and second guides are progressively separatedby a longer distance starting from the value Dc until they are separatedby a value of more than Ds, wherein the values Dc, Lc, W1 and W2 areselected so as to obtain an achromatic divider element at divideroperating wavelengths, and the values Dc and Lc are selected so that thefirst coupling type and the second coupling type vary inversely withsaid wavelengths.
 2. The divider according to claim 1, wherein the firstand second guides of the 2 to 2 divider element are single mode.
 3. Thedivider according to claim 1, wherein the substrate is glass and thefirst and second guides are made by ion exchange in the substrate. 4.The divider according to claim 1, wherein the first and the secondguides have widths W1 and W2, respectively, such that the 2 to 2 dividerelement is achromatic in operational spectral windows from 1260 to 1360nm and from 1480 to 1660 mm.
 5. The divider according to claim 1,wherein distances between the first and second guides varysymmetrically.
 6. The divider according to claim 1, wherein the value Dcis less than or equal to the value Dx, wherein Dx corresponds to adistance separating the first and second guides at which couplingbetween said guides changes from coupling in which longer wavelengthsare preferentially coupled to coupling in which shorter wavelengths arepreferentially coupled.
 7. The divider according to claim 1, wherein inthe first and third parts of the 2 to 2 divider element, the first andsecond guides are curved with a radius R≧Rc, or according to asinusoidal function with a minimum radius of curvature R≧Rc, where thevalue Rc is defined as a critical radius of curvature above which thereare substantially no curvature losses at a highest operating wavelength.8. The divider according to claim 7, wherein R=Rc.
 9. The divideraccording to claim 1, wherein the divider element operates in 1260-1360nm and 1480-1660 nm spectral windows and has a division ratio CR equalto 0.5, wherein the widths W1 and W2 are selected to vary from 1.6 μm toWc, wherein the distance Dc varies from 0.6 μm to 2.6 μm and the lengthLc varies from 0 μm to 450 μm, where Wc is the maximum width for whichthe first and second guides are single mode for said spectral windows.10. The divider according to claim 1, wherein n is greater than 2, andsaid divider comprises a 2 to 2 optical divider element and (n−2) 1 to 2cascaded divider elements such that the divider comprises two inputscorresponding to the first and second guides of the 2 to 2 dividerelement, and n outputs.
 11. The divider according to claim 10, whereinthe (n−2) 1 to 2 divider elements are selected from the group consistingof Y couplers, junctions and combinations thereof.